The invention relates to a large-area washer for fastening roofing sheets or the like.
Such a washer is known from U.S. Pat. Nos. 4,763,456 and 4,787,188.
Such washers are usually used to fasten single layers or multilayers of roofing sheets and/or an insulating layer on a solid foundation. In order to achieve appropriate fastening of the covering roofing sheet, points, which are aligned in the fastening direction, are provided at the underside of the large-area washer known from the U.S. Pat. No. 4,763,456 and indentations, pointing in the fastening direction, are provided at the underside of the large-area washer known from U.S. Pat. No. 4,787,188. The points and indentations are provided as protruding elements and thus are contacting elements, which pierce the roofing sheet. They are thus elements, which mesh with the roofing sheet without piercing it and thus merely increase the friction between the roofing sheet and the washer. Relatively high forces arise due to corresponding suction loads on the roofing sheet, so that the endeavor exists to pull out the roofing sheet under the fastener or under the washer. The elements, which protrude from the underside of the washers and improve the meshing or improve the friction, are intended to ensure a corresponding reliability of the fastening site.
On the other hand, the necessity exists of being able to make screwed connections on an inclined or flat roof by machine, for which some form of magazine for the screws as well as the washers is required. Since stacking represents the most effective type of magazining, also when regarded from the point of view of the space required, problems arise with the elements, which protrude from the washers. For singling the washers in appropriate screwing equipment, it is necessary that the washers, which are stacked on top of one another, or at least the washer at the bottom, can be shifted or twisted with respect to the stack above. The protruding elements, which are provided to increase the friction or the meshing, are an obstacle.
The same problem also exists with a known washer (German Auslegeschrift 12 69 840), for which indentations with tabs, which can also be an obstacle to the singling of washers stacked on top of one another, are provided as spacers.